Hydraulic servo-assisted steering system for vehicles and a controlling method for a steering system of this type

ABSTRACT

For a hydraulic servo-assisted steering system for motor vehicles, classifying storage of the respectively measured, actual valve characteristic curves is provided and, corresponding to this, energization characteristic curves for the magnetic actuator of the converter are provided, which may be paired in a classified manner in order to compensate for deviations from a predefined set valve characteristic curve, and a testing method for such a hydraulic servo-assisted steering system is provided, in which the loading pressure of the servo actuator is influenced as a function of an input steering torque and in a speed-dependent manner, the speed-dependent influence being effected via the electro-hydraulic converter, whose energization may be set in a manner superimposed on the speed-dependent definition with regard to the correction of tolerances.

FIELD OF THE INVENTION

The present invention relates to a hydraulic servo-assisted steeringsystem for motor vehicles and to a setting method for such a steeringsystem, e.g., for compensating for deviations, caused by productiontolerances, from a set steering behavior of such vehicle servo steeringsystems.

BACKGROUND INFORMATION

Servo-assisted steering systems of the above-mentioned type aredescribed, for example, in German Published Patent Application No. 42 20624. In these, the torque-dependent actuation of the servo actuatorassisting the steering force is controlled by a hydraulic steering valvein the form of a rotary slide valve. For this purpose, the rotary slideof the rotary slide valve is firmly connected to an input element formedby the steering shaft so as to rotate with it, and the input element isconnected so as to rotate with a limited rotational angle and dependenton the torque with respect to an output element connected to thesteering mechanism via a torsion spring. The output element is in turnfixed against rotation to a control bush which is coaxial with therotary slide and can rotate with respect to the latter. Depending on thetorque-dependent rotation of the control bush with respect to the rotaryslide, the result is different degrees of overlap between thecorresponding connection cross sections of these, and thus differentopening cross-sections in the feed and discharge of the servo actuator.The torque assistance via the torsion spring has speed-dependent torqueassistance superimposed on it and, for this purpose, the control bush isacted on axially at the end by a reaction piston which, in relation tothe input element and to the rotary slide, is supported firmly such thatit cannot rotate but can be displaced axially and is spring loaded inthe direction of the control bush. The mutually facing ends of thecontrol bush and of the reaction piston have displacement surfaces whichare inclined in opposite directions, between which there are rollingelements, so that, depending on the torque-dependent rotation of thecontrol bush with respect the rotary slide or the input element, as aresult of the rolling elements running onto the displacement surfaces,the result is a displacement of the reaction piston counter to the forceof the latter in the direction of the spring acting on the control bush.

The chamber which accommodates the spring is designed as a pressurechamber and is to be connected to the high-pressure side of thehydraulic circuit such that the reaction piston, assisting the loadingspring force, is pressure-loaded in the direction of the control bush,so that as the pressure increases, the assistance between input andoutput element becomes rotationally more stiff. The pressure supplied tothe reaction chamber is controlled as a function of speed via anelectro-hydraulic converter with an actuating magnet that acts on ahydraulic valve arrangement.

A steering valve of this type has an initial position at speeds aroundzero which corresponds to a position of maximum servo action, such as isdesired for parking, for example. Starting from this position, thesteering becomes rotationally stiffer with increasing speed as a resultof the superimposed pressure loading of the reaction piston, in the samedirection as he spring force, so that a higher input torque has to beapplied for steering movements. German Published Patent Application No.42 01 311 describes a servo-assisted steering system with the same basicstructure, but the steering valve has an initial position whichcorresponds to a position of minimum servo action, such as is theintention for higher speed, for example, in order to avoid a woollysteering feel by an appropriately rotationally stiff steering system,and to obtain improved feedback from the roadway. The reaction piston ispressurized in the direction opposite to the spring force as a functionof speed, specifically such that, at speeds around zero, the result isthe intended high servo action, in which the steering torque input onthe input side is assisted in a relatively rotationally soft mannerbecause the reduced stiffening of the torsion spring via thespring-loaded reaction piston as a result of the pressurization.

Depending on the initial position, therefore, the pressurization of thereaction piston can be used to adjust the steering system in the harddirection with increasing speed, with the pressurization in the samedirection as the spring force or, with pressurization in the oppositedirection, to make the steering system rotationally softer with reducingspeed, starting from its hard, rotationally stiff setting, as is desiredfor parking.

Irrespective of the respective constructional design in this regard, onthe steering valve side, as a result of the rotary slide and thesuperimposed, speed-dependently operating actuating and controlelements, a relatively long function chain with alternating influencesis provided and, irrespective of the testing and setting of theindividual functional elements, tolerances can occur which, inparticular in the context of mass production, lead to scatter withrespect to the respective valve characteristic curve, which also becomenoticeable in vehicles with the same equipment level and impart adifferent steering feel. Such mass-production scatter leads tocomplaints in the case of manufacturers of vehicles, and likewise in thecase of end customers, in particular if these are sensed as deviationsfrom the usual.

Since the checking of the steering in its entirety and in the overallassembly in the vehicle is barely possible with tolerable effort, but inparticular access to the hydraulic elements cannot be implementedwithout dismantling, it is necessary to fall back on specific settingdevices in testing the individual elements. With their aid, theelectro-hydraulic converter is set by mechanical intervention to aconverter characteristic curve which corresponds in the best possiblemanner to the set characteristic curve of the steering valve and which,therefore, as based on the effective coil current of the converter,results in a reaction pressure, i.e., a build-up of pressure in thereaction chamber partly bounded by the reaction piston, as a function ofspeed, which corresponds to the respectively intended servo actionillustrated by the set valve characteristic curve.

A calibration of this type of the electro-hydraulic converter isinfluenced as such by the tolerances of the associated setting deviceand in the pairing with the hydraulic valve arranged downstream, inparticular a rotary slide valve, has superimposed on it tolerances ofthe latter and those of a steering mechanism arranged downstream.Subsequent intervention possibilities, in the sense of readjustment bymechanical intervention in the hydraulic steering valve, are virtuallynot provided, and thus subsequent changes are at most possible withconsiderable effort.

It is an aspect of the present invention to provide for, e.g., withlittle effort, and, e.g., which may also be managed well in massproduction, limiting the tolerances in relation to the set valvecharacteristic curve associated with the intended steering behavior. Afurther aspect of the present invention is to provide a testing methodwhich may make it possible, e.g., with little effort and e.g., one whichmay also be managed well in mass production, of limiting the tolerancesin relation to the set steering characteristic curve associated with anintended steering behavior and of permitting the set valvecharacteristic curve corresponding to this.

SUMMARY

According to the an example embodiment of the present invention, aplurality of energization characteristic curves are assigned to theelectro-hydraulic converter and the dependence, expressed in the valvecharacteristic curve, between steering input torque, e.g., steeringwheel actuating torque, and the pressure also influenced by theelectro-hydraulic converter is used for the purpose of correctingdeviations from the set valve characteristic curve by pairing anenergization characteristic curve—from the family of possibleenergization characteristic curves of the converter—which may compensatein the best manner possible for the deviation of the current, e.g., theactual, valve characteristic curve, from the set valve characteristiccurve.

According to an example embodiment of the present invention, appropriateenergization characteristic curves of the electro-hydraulic converterand assigned to the controller or the converter may be stored orimplemented.

Immediate assignment to the controller offers the possibility, startingfrom the controller, of already energizing the converter in accordancewith the respective energization characteristic curve. Assignment to theconverter offers the possibility, starting from the latter, to call anenergization with a respectively predefined current intensity in thecontroller or, on the part of the converter, to vary the energizationpredefined by the controller in a corrective manner, it being possiblefor this purpose for the converter to be assigned hardware, for example,in the form of an appropriately populated adapter. Resistances which maybe connected or disconnected or else resistance networks may be suitablefor the population.

According to an example embodiment of the present invention, an aspectincludes classifying the hydraulic steering valve with respect to itsrespectively measured actual valve characteristic curve in the level ofthe deviation from the predefined set valve characteristic curve and,based on a family of energization characteristic curves provided on theconverter side, to make an assignment which, given appropriate pairing,may furnish a best possible approach to the respective set valvecharacteristic curve. As based on the range in which the deviations ofthe measured actual valve characteristic curve from the associated setvalve characteristic curve may usually lie, a family of energizationcharacteristic curves may be predefined of which individual ones in eachcase cover a classified deviation range from the set valvecharacteristic curve, so that the deviation range from the respectiveset valve characteristic curve as far as the excursion limit is coveredsegment by segment by an appropriate energization characteristic curvefor the converter, and a pairing classification is made possible, whichmay lead to far-reaching compensation of the respectively measureddeviation from the set valve characteristic curve and, as a result, maynarrow the given tolerance band substantially.

The classification, in each case determined by measurement, for thedeviation on the part of the steering valve from the set valvecharacteristic curve is stored assigned to the steering valve, so that,following the installation of the steering valve in the vehicle andproduction of the electrical connection to the controller, which may beprovided on the vehicle side, a pairing of respective, classifiedcharacteristic curves may be carried out automatically in an automatedmanner.

This is also possible in the case of an assignment predefined inhardware of energization characteristic curves, for example in anadapter plug to the converter, if, by feeding in the classificationsignal associated with a respective actual valve characteristic curve,the hardware configuration assigned to the corresponding energizationcharacteristic curve is activated.

An example embodiment of the present invention includes a testing methodin which, based on a predefined vehicle speed, the loading pressurecorresponding to an actual valve characteristic curve is equalized tothe set loading pressure by changing the current intensity of thecurrent flowing via the actuator, and in which a correspondingcalibration is carried out via the speed-dependent energization of theactuator.

According to an example embodiment of the present invention, thisequalization may be carried out on the basis of one or more set valvecharacteristic curves predefined as a function of speed and, with regardto the respective valve characteristic curve, at one or more points,equalization at a point with regard to the respective actual valvecharacteristic curve to the set valve characteristic curve, inconsideration of the only slight offset of the characteristic curvesrunning substantially in the same direction, proving to be adequate as arule and leading to an approximation to such an extent that remainingdeviations which do exist may be tolerated.

If the steering valve and the associated hydraulic converter are treatedas one test unit, then the energization of the converter predefined bythe controller—given storage on the converter side of a convertercharacteristic map with the coordinates including vehicle speed, inputsteering torque and electrical resistance, etc.—may be varied as afunction of the respectively provided input steering torque and based onthe respective speed such that the set steering behavior may beachieved, that is to say, via appropriate changing of the predefinedenergization, the loading pressure corresponding to the set valvecharacteristic curve may be achieved. However, the measurement of theinput steering torque needed in the case of this procedure may entail acertain amount of effort.

A simplified procedure may be provided if the valve characteristic curveis considered as the superimposition of a hydraulic and an electriccharacteristic curve, the hydraulic characteristic curve beingconsidered to be predefined by the mechanical design of the valvecomponents with their tolerances. The electrical characteristic curve isviewed as a characteristic curve dependent on the speed of travel as aresult of energizing the converter. If, based on a test unit includingsteering valve with electro-hydraulic converter, the converter currentis stored based on a given steering torque against the speed of travelwhen moving along the valve characteristic curve corresponding to a setsteering characteristic curve, then the energization characteristiccurve of the converter may already contain the correction factor whichtakes into account the effect of the mechanical tolerances provided inrelation to the test unit. Therefore, the necessity for torquemeasurement may be dispensed with, and the result is a pressure loadingwhich may approach the set valve characteristic curve closely.

This correspondence may be all the more complete the more accurately arespective set valve characteristic curve is moved over via a speed oftravel, the accuracy, based on a speed-dependent set valvecharacteristic curve covered, being greater the greater the number ofpoints moved to on the set valve characteristic curve.

An example embodiment of the present invention includes a method thatincludes making use of the largely corresponding characteristics of thespeed-dependent set valve characteristic curves and also thetolerance-induced actual characteristic curves respectively provided forthis purpose and, starting from this point, restricting the testing andsetting method with regard to the equalization at one or more settingpoints of the input steering torque and, based on the respective settingpoint, bringing about the corresponding equalization by changing theenergization of the converter at this point, under the premise that, inaccordance with the largely corresponding shape of the set valvecharacteristic curves and also their associated, tolerance-inducedactual characteristic curves, a correction based on the correction valuedetermined point by point of the energization furnishes an adaptation ofthe respective actual characteristic curve to the corresponding setvalve characteristic curve far-reaching improvements such that anyremaining, tolerance-induced deviations may in practice no longer benoticeable as deviations in the steering behavior.

Further details and features of example embodiments of the presentinvention are set forth below, with reference to the appended Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates, in a schematic overall view, a hydraulicservo-assisted steering system for motor vehicles, including ahydraulic, torque-dependency operating valve and an electro-hydraulicconverter assigned to the latter for speed-dependent activation.

FIG. 2 is a basic illustration of an electro-hydraulic converter in verysimplified form.

FIG. 3 illustrates a characteristic curve graph for hydraulicservo-assisted steering systems for motor vehicles as illustrated inFIG. 1 in schematic form, from which the actuating pressure acting onthe servo actuator of the servo-assisted steering system results fromthe respective set valve characteristic curve associated with a speed bythe input torque predefined on the steering wheel side.

FIG. 4 is a further simplified, schematic, graphical illustrationaccording to FIG. 3 with assignment of the respective converterenergization to the set valve characteristic curves.

FIG. 5 illustrates a valve characteristic curve, measured during thechecking of a steering valve on a test bench, in association with thecorresponding set valve characteristic curve, in an illustrationcorresponding to FIG. 4.

FIGS. 6 and 7 illustrate schematic characteristic maps in which theenergization of the converter (energization characteristic curves)corresponding to the intended pressure variations (set valvecharacteristic curves) intended on the valve side or actuator side areplotted against the speed.

FIG. 8 illustrates a characteristic curve graph for a hydraulicservo-assisted steering system for motor vehicles in schematic form inwhich—as theoretical set points—the actuating pressure acting on theservo actuator of the servo-assisted steering system for associatedspeeds is plotted against the input torque predefined on the steeringwheel side.

FIG. 9 illustrates, based on a graphical illustration according to FIG.8 and accordingly in a speed-dependent manner, set valve characteristiccurves with the energization stipulations correlating with the speedinformation according to FIG. 8 for the electro-hydraulic converterwhich is assigned to the steering valve of the hydraulic servo-assistedsteering system.

FIG. 10 shows, in an illustration corresponding to FIG. 9 but highlyexaggerated, a valve characteristic curve corrected during thetest-bench checking of a steering valve via the energization of theconverter to a set valve characteristic curve, in order to illustratethe sequence provided in the valve test bench.

FIG. 11 is a schematic block diagram illustration of the test-benchdetermination of the tolerance-corrected energization characteristiccurve of the converter.

DETAILED DESCRIPTION

FIG. 1 is a schematic overall illustration of parts of a servo-assistedsteering system for vehicles. Reference character 1 designates thesteering wheel via which—as input torque—the respective steeringcommands are input by the driver. These steering commands aretransmitted, with the assistance of an articulated steering shaft 2, toa hydraulic steering valve 3 which, for example, in the configuration asa rotary slide valve, drives a servo actuator 4 as a function of torque.Via the latter, the steering forces exerted on the steering wheel 1 andtransmitted via the steering mechanism 5 are modulated in an assistingmanner as a function of predefined parameters, for example, as afunction of torque and speed.

The steering mechanism 5 in the scheme illustrated in FIG. 1 is designedas a rack and pinion steering system. The servo actuator 4 extends as apiston actuator approximately in the direction of the rack extendingtransversely with respect to the vehicle between the steerable wheels.The rack meshes with a pinion, which is connected to the output elementof the hydraulic, torque-dependently operating steering valve 3.

The hydraulic pressure supply is provided via a pressurized oil pump 6which, with the oil reservoir 7, is located in a hydraulic supplycircuit 8 which leads via the steering valve 3 to the servo actuator 4.

Assigned to the steering valve 3 is an electro-hydraulic converter 9,via which speed-dependent, hydraulic loading of the steering valve 3 iscarried out superimposed on its torque-dependent loading. The converter9, as shown in the schematic illustration according to FIG. 2, includesa hydraulic valve 17 and an actuating magnet 16 which acts on the latterand, as shown in the overall illustration according to FIG. 1, isaddressed via a controller 10. The controller 10 converts the speed oftravel V registered by the tachometer 11, e.g., electronic tachometer,into actuating signals for the actuating magnet 16 of the converter 9.

The functions in this regard may be taken, for example, from GermanPublished Patent Application No. 42 20 624, as may the configuration ofthe valve 3 as a rotary slide valve, in which the torque-dependentpressure supply of the servo actuator 4 has superimposed on it aspeed-dependent actuation such that the servo action in principledecreases with increasing speed, as illustrated in FIG. 3, in which thepressure P applied to the servo actuator 4 and modulated as a functionof speed by the converter 9 is plotted against the input torque M.

FIG. 3 illustrates that, at low speeds Vmin, an intense servo action isprovided, and that this servo action is reduced toward the maximum speedso that, in the region of low speeds, e.g., during parking, in spite ofhigh opposing forces, the result is soft steering, assuming only lowinput torques, while the steering is stiffened increasingly toward highspeeds, in order to ensure a direct steering feel even under thesedriving conditions.

In the configuration mentioned, the steering valve 3, as a rotary slidevalve, has a basic structure, e.g., in a conventional manner, in which arotary slide fixed to the steering shaft 2 so as to rotate with it isprovided and is enclosed by a steering bush which, with respect to thesteering shaft 2, is supported by a torsion spring such that it mayrotate to a limited extent and which is produced via the driveconnection to the steering mechanism 5. With regard to thetorque-superimposing, speed-dependent activation of the steering valve,the control bush may be loaded axially via the converter 9 via areaction piston which is fixed to the rotary slide and therefore to theinput shaft so as to rotate with it and which is spring-loaded in thedirection of the facing end of the control bush, there being between theends displacement elements via which, during rotation of the reactionpiston with respect to the control bush, the reaction piston isdisplaced axially by the control bush.

As a function of the force exerted axially in the direction of thecontrol bush via the reaction piston, this arrangement results in thepossibility of influencing the rotational stiffness of the steeringsystem since, with increasing axial loading of the displacement elementsbetween control bush and reaction piston, a torque is built up whichacts as a supplement to the torsion spring and therefore counter to thedirection of rotation of the control bush via the input torque.

The force loading the reaction piston axially in the direction of thecontrol bush may be increased as a function of speed via the converter,by the reaction piston being loaded hydraulically in the direction ofthe control bush. A solution of this type is described in GermanPublished Patent Application No. 42 20 624.

In the case of another solution, described in German Published PatentApplication No. 42 01 311, constructionally, by appropriatespring-loading of the reaction piston, a high axial bias of the reactionpiston toward the control bush may be provided, so that, inconstructional terms, stiff steering is predefined, as is the intentionat higher speeds, and, via the hydraulic loading controlled by theconverter, the reaction piston is displaced counter to the loading forceof the spring when soft steering, e.g., steering with high servoassistance is intended, for example, in the parking range.

Such a configuration described in German Published Patent ApplicationNo. 42 20 624 is assumed for the following explanation of an exampleembodiment of the present invention, in which, corresponding to the highservo action at low speeds, a pressure loading is predefined via theconverter 9 by appropriately high energization of the magnetic actuator16. This therefore also means that, when the energization fails, theservo action is omitted and therefore, in hazardous speed ranges, theusual, stiff steering behavior is substantially maintained.

The schematic illustration in FIG. 3, in which the actuating pressure Pwhich is applied as a function of an input torque M established as setvalve characteristic curves, based on a constant speed in each case,reveals that, at a minimum speed Vmin lying around zero, a high servoaction is provided, so that easy steering is implemented in the parkingrange by high servo assistance, while the steering becomes increasinglytighter toward the maximum speed Vmax

FIG. 4 illustrates, highly schematically and in a manner analogous toFIG. 3, the valve characteristic curve shapes given for one speed ineach case at the energization of the converter corresponding to therespective speed. The energization is greatest with Imax in the parkingrange and reduces toward Imin, corresponding to the maximum speed rangeVmax, with decreasing servo action according to the initial situationexplained above.

The speed-dependent variation which is illustrated in FIGS. 3 and 4 ofthe servo action dependent on the input torque M is therefore providedvia appropriate energization of the actuating magnet 16 which isassigned to the converter 9, is connected via a connection 13 and a lineconnection 14 to the controller 10 and which has an armature 15 whichpasses through a coil 12 and an iron core 18 and is loaded via a spring19 such that, when there is no energization of the actuating magnet 16,the valve 17 is open.

The fundamentally speed-dependent energization of the actuating magnet16 is used in order, e.g., to compensate for tolerance-induceddeviations of the steering valve 3 and scatter caused by this in thesteering behavior, which is illustrated schematically in FIG. 5, inwhich, corresponding to the illustration in FIG. 4, 20 designates a setvalve characteristic curve, while at 21, an actual valve characteristiccurve corresponding to the set valve characteristic curve 20 andrecorded on the test bench at the conclusion of the valve assembly isillustrated. The arrow 22 indicates the correction necessary tocompensate for the deviation between the actual valve characteristiccurve 21 and the set valve characteristic curve 20.

For this purpose, FIGS. 6 and 7 illustrate two possibilities, namely inFIG. 6 a general increase in the energization, e.g., the currentintensity over the speed, performed in accordance with the deviationaccording to arrow 22, the actual valve characteristic curve 21 in FIG.5 corresponding to an energization characteristic curve 23 which, byraising the energization according to arrow 24, is transferred into anenergization characteristic curve 25 which is selected such that, onaverage, the result may be the best possible approach of the actualvalve characteristic curve 21 to the set valve characteristic curve 20according to FIG. 5 and the pressure variation corresponding to this.Such a general increase may be achieved by hardware, for example, by anappropriately increased current being provided by the controller or byan appropriate increase in the current flowing via the coil 12 beingproduced by the magnetic actuator, for example, by severing at least oneresistance provided in a parallel circuit with the coil 12.

FIG. 7 illustrates a further possibility of operating with acharacteristic map, of which in each case that energizationcharacteristic curve is activated which may be suitable to adapt themeasured actual situation in the best possible manner to the desired setsituation by changing the current intensity.

For the practical procedure, it may be provided to register therespective test-bench result for the unit including steering valve 3 andconverter 9 as an actual valve characteristic curve, to classify it withregard to the level of deviation from a predefined set valvecharacteristic curve and to “provide the respective classificationtogether” with the respective assembly unit, e.g., provide it togethersuch that they may be called up. Corresponding to the selectedclassification, e.g., by the controller or by the actuating magnet 16, alevel of equipment is provided which, corresponding to the respectiveclassification, leads to pairing of a corresponding, correctiveenergization. This pairing may be carried out in an automated manner if,during the assembly of the steering system, this is installed with thesteering valve in the respective vehicle and is connected appropriately.

During the connection, the classification result which, for example, isstored in a memory module 28, as indicated schematically in FIG. 2, maybe transmitted to the controller 10 or else to the adapter 27, ifappropriate adaptation of the current intensity is only performed viathe adapter 27.

The following description of the test-corrected and tolerance-correctedsetting method for a hydraulically operating vehicle servo steeringsystem relates to a configuration of such a servo steering system asdescribed, for example, in German Published Patent Application No. 42 20624, in which the steering valve provided is a rotary slide valve, whichis located in the activation of a servo actuator and via which thepressure supply of the servo actuator is provided as a function of theinput steering torque, as a function of the torque and, superimposed onthis, as a function of speed, e.g., in principle such that the servoaction decreases with increasing speed. The speed-dependent pressurecomponent is provided via an electro-hydraulic converter, which isenergized as a function of speed.

For the steering valve, various designs are possible, as illustrated,for example, in the aforementioned German Published Patent ApplicationNo. 42 20 624 and German Published Patent Application No. 42 01 311. InGerman Published Patent Application No. 42 20 624, the speed-dependentpressure component is used—by increasing the energization in a mannercorresponding to the rising speed—to stiffen the steering, which is softin the basic mechanical deflection at low speeds, for example in theparking range, in a manner corresponding to the rise in the speed, byincreasing pressurization via the electro-hydraulic converter. GermanPublished Patent Application No. 42 01 311 follows the converse routeand provides a hard mechanical basic configuration which, in the rangeof lower speeds, for example in the parking range, is made soft by thepressure component provided via the electro-hydraulic converter, and inwhich, accordingly, in order to harden the steering toward high speeds,the pressure component provided via the electro-hydraulic converter isreduced.

The schematic illustration according to FIG. 9 starts from such asolution, in which, corresponding to the illustration according to FIG.8, speed-dependent valve characteristic curves are assignedcorresponding, and therefore also speed-dependent, energizationstipulations, the valve characteristic curve of minimal energizationcorresponding to the valve characteristic curve of maximum speed, andvice versa.

For the testing and setting method according to an example embodiment ofthe present invention, which is shown in the scheme illustrated in FIG.11 and which will be explained below, the speed-dependent energizationof the electro-hydraulic converter is used as a starting point for thecorrection of tolerance-induced deviations from the (theoretical) setvalve characteristic curve (FIG. 8) corresponding to the respectivelypredefined steering characteristic curve. The given (theoretical)loading pressure P1 of the servo actuator, based on a predefined speedof travel V1 and an input steering torque M1, as a set point is observedfor deviations and any deviations are compensated for by correcting theconverter current.

FIG. 8 illustrates, in dashed lines and schematically, in relation to aset valve characteristic curve V1 given on the basis of a vehicle speedV1, an actual valve characteristic curve V1′ resulting from thetolerances mentioned, so that a loading pressure P1′ based on the sameinput steering torque results.

FIG. 9 illustrates the valve characteristic curves corresponding to theset point curves, e.g., the respective (theoretical) set valvecharacteristic curves according to FIG. 8 with energization correlatingwith the respective speed, one of these characteristic curves,corresponding to the set valve characteristic curve V1 in FIG. 8, beingdesignated 11. As illustrated, the loading pressure P therefore changesin a manner corresponding with the speed as a function of theenergization of the converter corresponding to this speed and the inputsteering torque.

FIG. 10 illustrates that, based on the same input steering torque, theloading pressure P may be varied by changing the current intensity, forexample, therefore, the tolerance-induced change in the loading pressurefrom P1 to P1′. in spite of an energization I1 corresponding to the setvalve characteristic curve V1 may be compensated for by changing theenergization of the converter, based on the illustration according toFIG. 10, by raising the current intensity I1 to a current intensity I,or which is higher than the current intensity I1 corresponding to theset valve characteristic curve V1 and which, compensating for thetolerances, guides the loading pressure back from P1, to P1.

The current flowing via the converter therefore forms and actuatingvariable via which, in a manner fed back to the respectively definedvehicle speed and the predefined input steering torque, a pressureloading of the servo actuator may be achieved which corresponds to thetheoretical set predefinition, e.g., the set valve characteristic curve,at least to a good approximation.

An appropriate, correction, based on a respective speed of travel, maybe stored for any desired speed of travel in that, in the testingmethod, the converter current is stored dynamically as a function of thespeed of travel based on the respective set valve characteristic curve,so that in the superimposition of the energization characteristic curveon the mechanical-hydraulic actual characteristic curve provided as afunction of the input steering torque, a close approximation to thetheoretical set characteristic curve may be achieved.

The appropriate storage of the corrected energization value may becarried out both in the controller and also assigned to the converter,the latter representing an example embodiment of the present inventionsince, based on the unit including steering valve with converter,irrespective of the respective energization predefinition via thecontroller, the energization may be adapted individually by theconverter, which may permit standardized vehicle-side presetting of thecontroller and compensation for inaccuracies occurring on the basis ofthis presetting in the respective testing unit by the correction storedon the converter side and based on this presetting, and thus this may betaken directly into account when the tested unit is mounted in thevehicle. Appropriate correction values, paired with respect to theconverter, may also be downloaded to the controller, e.g., with aconnection in the vehicle, in order subsequently to achieve a“corrected” energization of the converter directly via the controller.

In the extreme case, the setting and testing method according to anexample embodiment of the present invention may also permit operationwith only one measured point with regard to a predefined speed andtransfer of the corrective change in the energization of theelectro-hydraulic converter, to be performed with regard to thismeasured point in general in a corrective manner, to the respectivevalve characteristic curve, since the speed-dependent curve shapes arein principle, e.g., with regard to the curve curvature, predefined bythe mechanical-hydraulic behavior of the steering valve, and thetolerance-induced deviations are relatively small and barely influencethe curve shape in its characteristics.

However, it also within the scope of an example embodiment of thepresent invention, based on the valve characteristic curve given for aspeed, to move to a plurality of measured points and to perform anappropriate calibration in an interpolating manner, so that thetheoretical valve characteristic curve, e.g., the respective set valvecharacteristic curve, is met in a still better arrangement, a procedureof this type based on a plurality of valve characteristic curves beingexemplary.

An example embodiment of the present invention therefore may provide atesting and setting method for hydraulically operating vehicle servosteering systems in which the loading pressure of the servo actuator isinfluenced as a function of an input steering torque and as a functionof speed, the speed-dependent influence being carried out via anelectro-hydraulic converter, whose energization may be set with regardto the correction of tolerances superimposed on the speed-dependentdefinition, so that compensation of tolerance-induced deviations fromthe set predefinitions may be possible with little effort.

1. A hydraulic servo-assisted steering system for a motor vehicle,comprising: an electro-hydraulic converter; a steering-force-assistingservo actuator; a controller; and a hydraulic steering valve configuredto control, as a function of torque and speed superimposed by thecontroller, hydraulic loading of the steering-force-assisting servoactuator by the electro-hydraulic converter; wherein the steering valveincludes a set valve characteristic curve corresponding to a setsteering behavior of the steering system, the electro-hydraulicconverter including an actuating magnet configured to energize thesteering valve in a manner oriented to the set valve characteristiccurve, at least one of (a) the controller, (b) the electro-hydraulicconverter, and (c) the actuator configured to store a plurality ofenergization characteristic curves assigned to the actuating magnet, anenergization characteristic curve adapted to correct deviation of arespective actual valve characteristic curve from the set valvecharacteristic curve corresponding to the set steering behavior beingconnectable.
 2. The hydraulic servo-assisted steering system accordingto claim 1, wherein the controller is configured to store theenergization characteristic curves assigned to the actuating magnet. 3.The hydraulic servo-assisted steering system according to claim 1,wherein the energization characteristic curves stored by one of (a) thecontroller and (b) the electro-hydraulic converter are assigned to anadapter.
 4. The hydraulic servo-assisted steering system according toclaim 3, wherein the adapter is assigned to the actuating magnet.
 5. Thehydraulic servo-assisted steering system according to claim 1, whereinthe respective actual valve characteristic curve of the steering valveis classified.
 6. The hydraulic servo-assisted steering system accordingto claim 1, wherein the respective actual valve characteristic curve ofthe steering valve is classified with respect to a deviation from theset valve characteristic curve of the steering valve.
 7. The hydraulicservo-assisted steering system according to claim 1, wherein theenergization characteristic curve of the actuating magnet is classified.8. The hydraulic servo-assisted steering system according to claim 1,wherein the energization characteristic curve of the actuating magnet isclassified with respect to a deviation from the energizationcharacteristic curve corresponding to the set valve characteristiccurve.
 9. The hydraulic servo-assisted steering system according toclaim 1, wherein classification values corresponding to the actual valvecharacteristic curves and the energization characteristic curves arepaired with one another.
 10. The hydraulic servo-assisted steeringsystem according to claim 1, further comprising an arrangementconfigured to store classification values of the actual valvecharacteristic curves and correspondingly corrective energizationcharacteristic curves assigned to one of (a) the steering valve, (b) theconverter and (c) the controller, to activate the classification valuesduring mounting and to pair the classification values to call oneanother.
 11. The hydraulic servo-assisted steering system according toclaim 1, wherein the one of (a) the controller, (b) the converter, and(c) the actuator is configured to store the energization characteristiccurves digitally.
 12. The hydraulic servo-assisted steering systemaccording to claim 1, further comprising an arrangement configured tovary the energization characteristic curves by connectable hardwareconfigurations.
 13. A method for a hydraulic servo-assisted steeringsystem, comprising: performing hydraulic pressure loading of a servoactuator by a steering valve; adjusting a loading pressure correspondingto a set valve characteristic curve; processing vehicle speed as aninput variable; defining the loading pressure as a function of an inputsteering torque and vehicle speed superimposed on the steering torque;acting on an electro-hydraulic converter with a current intensity thatcorresponds to the vehicle speed; equalizing based on a predefined speedof travel the loading pressure corresponding to an actual valvecharacteristic curve to a set loading pressure by changing the currentintensity of current flowing via the electro-hydraulic converter; andperforming a corresponding calibration in relation to speed-dependentenergization of the electro-hydraulic converter.
 14. The methodaccording to claim 13, wherein the method is configured to compensatefor deviations induced by production tolerances from a set steeringbehavior of a vehicle servo steering system.
 15. The method according toclaim 13, wherein the vehicle speed is processed in the processing stepin a controller.
 16. The method according to claim 13, furthercomprising equalizing the actual valve characteristic curve and the setvalve characteristic curve based on the predefined speed of travel. 17.The method according to claim 13, further comprising equalizing theactual valve characteristic curve and the set valve characteristic curvebased on a plurality of predefined speeds of travel.
 18. The methodaccording to claim 13, wherein the calibration is performed on acontroller side.
 19. The method according to claim 13, wherein thecalibration is performed on a converter side.